The transport of gluscose from blood to cerebrospinal fluid is being studied under conditions of altered CSF formation rate. The proposition being examined is that glucose concentration is determined by the choroid plexus, and that the deficient CSF glucose content with regard to the blood is caused by the removal of a portion of CSF glucose by the choroid plexus. CSF formation is altered by (1) cerebral ventricular perfusion of -or the intravenous infusion of- anisosmotic mannitol solutions; (2) addition of oubain or diamox to the perfusion fluid. The effects of these experimental procedures on CSF formation and glucose influx rates will be compared. Each animal will serve as its own control, perfused with mock CSF prior to changing the contents of the perfusion fluid or intravenous infusion. In addition, changes in serum and effluent fluid glucose concentrations will be monitored to determine how rapidly the change in the former is followed by a change in the latter. Experiments are continuing to determine how closely choroid plexus blood flow changes correspond to those of the brain. Microspheres are used after threading a cannula up the femoral artery and into the left ventricle.